Biophysical measurements will be made of the heat production of non- myelinated nerve fibers during and soon after the impulse, together with electrical measurements of the post-tetanic hyperpolarization (which reflects the activity of the sodium pump, and pharmacological measurements of the interaction of drugs with the nerve membrane (tetrodotoxin, saxitoxin, local anesthetics). These measurements will all be used in an integrated approach to the molecular basis of conduction and of the subsequent recovery processes in mammalian nonmyelinated nerve fibers. These fibers, because of their small size, have a large surface/volume ratio and hence are extremely suitable for such a study.